Fluidic nondestructive memory



June 17 1969 T. D. READER 3,450,340

FLUIDI C NONDESTRUCTIVE MEMORY Filed Sept. 29, 1967 United States Patent York Filed Sept. 29, 1967, Ser. No. 671,730 Int. Cl. G11c 25/00; F15c 4/00 US. Cl. 235-201 4 Claims ABSTRACT OF THE DISCLOSURE A resiliently deformable memory element, comprising a drop of a liquid having high surface tension, is mounted within a chamber having two subchambers joined by a restricted passage through which the element can pass only with deformation, forming a bistable memory unit. The memory element is shiftable between subchambers by application of a fluid pressure diiferential between them. Once positioned, the element is stable, retaining the stored information independently of continuing porwer application to the system. The stored information is read in terms of the flow throughone or more sensing pas sages that open into the chamber in such position that the flow varies critically with the position of the memory element.

This invention has to do generally with fluid state computing systems and related devices for processing digital information. More particularly, the invention concerns fluid state memory systems that are non-destructive in the sense that complete loss of power from the system does not destroy the information that has been stored in the memory.

Each of the memory elements of the invention is typically a normally spherical fluid mass having high surface tension which is contained in an elongated chamber having a constriction or neck intermediate its length which divides the chamber into two subchambers between which the drop can pass only if distorted from its normal spherical form. The memory element is typically a drop of a liquid in gas, or a bubble of gas in liquid having high surface tension and having a surface such that it does not wet the chamber wall. Mercury is a satisfactory material for that purpose, and other liquids such as glycerine may be used with suitable surface treatment of the drop or of the chamber wall, or both. Information is stored in such a memory unit by applying a differential fluid pressure between the two ends of the chamber, forcing the body to move through the neck in the direction of the pressure gradient. Once the body has passed through the neck, the control signal pressure may be removed and no further power is required to maintain the stored information.

The stored information may be read in many different ways. For example, sensing ports are provided on opposite sides of one or both of the subchambers in such position that fluid can flow freely between them only when the body is in the other subchamber. The stored information is then read in terms of the flow or non-flow between such sensing ports in response to a reading pressure difference applied between them. If the memory element is a drop of a conductive liquid such as mercury, its presence or absence in one of the subchambers can be sensed in terms of electrical current flow between electrodes suitably placed in the subchamber wall, or by detecting any suitable electrical phenomenon that is selectively responsive to the presence of a conductive body within the subchamber.

A full understanding of the invention and of its further objects and advantages will be had from the following description of an illustrative manner in which it may be carried out. The particulars of that description, and of the accompanying drawings which form a part of it, are intended only as illustration and not as a limitation upon the scope of the invention, which is defined in the appended claims.

In the drawings:

FIG. 1 is a schematic section representing an illustrative memory unit in accordance with the invention;

FIG. 2 is a section on line 2--2 of FIG. 1; and

FIG. 3 is a series of schematic sections corresponding to a portion of FIG. 1 and illustrating different stages of operation of the memory unit.

A typical memory unit comprises structure forming a memory chamber and passages communicating with the chamber for supplying pressure pulses of sufiicient duration to actuate the contained memory element and for sensing the position of the memory elements to read the stored information. As shown illustratively in FIG. 1, the elongated memory chamber 12 is formed in a solid block 10, typically of transparent plastic material. Chamber 12 is partially divided by the annular constriction 18 into the two subchambers 14 and 16, which are typically of equal size and shape. The control passages 15 and 17 open into the opposite end portions of the respective subchambers .14 and 16, and are shown for clarity of illustration as coaxial with the chamber axis 19. Block 10 may be constructed of a plurality of layers, superposed and rendered effectively unitary by cement, diffusion bonding or polymerization in accordance with known practice for constructing fluid state amplifiers. The passages are indicated for clarity as having essentially circular sections, but any convenient shapes may be used.

The memory element 20 is a body of resiliently deformable material such as a fluid with high surface tension contained in chamber 12 and of such size that it is receivable in either subchamber and can move through constriction 18 from one subchamber to the other only by virtue of deformation. Element 20 may substantially till the cross-section of whichever subchamber it is in, as illustrated in FIGS. 1, 3A and 3D. For clarity of description element 20 is represented in the drawings as a liquid body immersed in a gaseous medium. However, element 20 may comprise a bubble of gas, such as nitro gen or air, for example, immersed in a liquid which typically occupies the remainder of the passage structure of FIG. 1. In either case, surface tension at the interface between liquid and gas tends to prevent deformation of the element.

Pressurized fluid for operation of the system is supplied from a suitable source, not explicitly shown, via the power inlet 24. A restricted amount of flow from inlet 24 is supplied via the resistance 26 to the branch conduit 27 and thence via the parallel resistances 2'8 and 29 to the respective control chambers 30 and 31. Those chambers open directly to the respective control passages 15 and 17, and also communicate via the respective normally open control valves 32 and 33 with a fluid sink, shown typically as atmospheric pressure. When those valves are both open, the fluid pressures in control chambers 30 and 31 are equal and are substantially atmospheric due to the flow limiting resistances 26, 28 and 29. Hence there is virtually zero flow through control passages 15 and 17, and memory element 20 remains stably in one or other of the subchambers.

When either of the control valves 32 and 33 is closed, pressure in the corresponding control chamber 30 or 31 increases rapidly to the pressure in branch conduit 27, producing a pressure level that is transmitted through the control passage 15 or 17 to one end of memory chamber 12, the other end of the chamber remaining at substantially atmospheric pressure. The resulting pressure differential between the ends of chamber 12 exerts a longitudinal force on memory element 20, which acts as a piston in the chamher. If such a pressure signal enters the subchamber containing the memory element, the latter is urged toward constriction 18. As the element reaches that constriction it becomes deformed, passing through a series of configurations such as that in FIG. 3B. In that form, the surface tension at the surface portion 40, having the relatively small radius of curvature r, produces a higher pressure within element 20 than does the suuface tension at the region 42, having the larger radius of curvature R. To move element 20 further to the right, that pressure difference must be overcome by the differential pressure within the two subchambers. As the symmetrical configuration of FIG. 3C is approached, the surface forces come into equilibrium. Once the majority of the volume of element 20 has passed the plane of symmetry of constriction 18, the surface tension produces a net forward force, tending to cause the element to pop through the orifice into the other subchamber, as in FIG. 3D. The control signal may then be removed, and no further power is required to maintain the memory element stably in its new state. Thus, switching of the memory element from one state to the other is accomplished in response to a control pressure pulse which in practice may be very brief. The memory unit is thus bistable in the usual sense of that term. Return of the memory element to its first state requires application of a signal pulse to the opposite end of chamber 12.

The memory unit of FIG. 1 includes the sensing passage 36, which opens into subchamber 16 at a point such tha the passage mouth is effectively blocked bymemory ele ment 20 when in that subchamber. Sensing passage 36 is supplied with pressurized fluid from a suitable source, and means are provided for discriminating between the flow conditions in presence and in absence of element 20 in subchamber 16. As shown, fluid supply for sensing passage 36 is derived from main inlet 24 via the flow limiting resistance 52 and the conduit 53. A restricted passage 54 of suitable resistance connects conduit 53 to atmospheric pressure, thereby limiting the maximum sensing pressure that can be applied at passage 36 to a valve typically well below the signal pulses applied at passages 15 and 17 for storing information in the memory unit. Hence pressure input at sensing passage 36 cannot affect the information storage function of the device. However, the pressure within conduit 53 is distinctly higher when sensing passage 36 is blocked by presence of the memory element in subchamber 16 than when passage 36 is opened by presence of element 20 in subchamber 14. 'Flow from sensing passage 36 may leave subchamber 16 via control passage 17 and open control valve 33, for example; or a special exit passage for the sensing flow may be provided, as indicated at 56. By suitable proportioning of passage 56 and the other described pasages, readout can be made essentially independent of the control pulses applied via passages 15 and 17. Normally, however reading from and writing into a memory do not occur simultaneously.

The described pressure difference in conduit 53 may be detected or indicated in any desired manner, as by connecting via the passage 59 a pressure transducer or a visual gauge, as indicated at 60. Device 60 may comprise a fluidic or flueric amplifier, preferably of bistable or flipflop type, which draws only negligible flow from conduit 53 and controls a larger power flow by which a desired control function is performed, for example. Such a sensing or readout system may be provided for both subchambers of the memory unit.

Readout device 60 may be connected, if preferred, to the outlet of passage 56, rather than to conduit 53. With that ararngement the output signal is inverted, since the sensed flow is greater in absence of memory element 20 in subchamber 16 and is essentially zero in presence of the element there.

Control valves 32 and 33 may be replaced, if preferred, by flow control means at passages 28 and 29, the open outlets 34 and 35 then being closed partially or entirely. In general, control pressure pulses for opearting the memory unit may be provided selectively to control passages 15 and 17 in any suitable manner, for example by direct connection of those passages to an output of respective fluid amplifiers, so that each passage receives pressure flow only when a signal is supplied to the associated amplifier. A memory unit is generally required for each bit" of stored information, and a plurality of such units can be combined in essentially conventional fashion to form systems for handling information of any required degree of complexity. A fluid amplifier controlled by the output of one memory unit or system can control in turn the input to another memory unit or system either directly or via computing logic of any required type.

The detailed form and proportions of chamber 12, and especially the size of constriction 18, may be varied within wide limits to provide the desired performance characteristics. For example, the smaller constriction 18, the more stable the memory unit against such spurior effects as accidental pressure pulses and bodily acceleration of the entire assembly. If memory element 20 is a dorp of liquid, the effective surface tension must be sufficient to hold the drop together as it passes through constriction 18, and to provide the required stability of the bistable system. Passages opening into chamber 12, such as the control and sensing passages that have been described, preferably have mouths small enough that the existing surface tension of element 20* prevents it from entering such passages under the maximum pressure differentials that can occur. In general, with a mercury drop as memory element, a preferred diameter for constriction 18 is of the order of two-thirds that of the subchambers, with the passage mouths less than one-third the chamber diameter. The entire unit can be scaled down almost without limit to reduce its weight and bulk, and to increase its insensitivity to high acceleration or shock loads.

I claim:

1. A memory unit for a fluid state computer comprising structure forming an elongated chamber having a constriction intermediate its length defining two subchambers,

a unitary body consisting essentially of glycerine in the chamber of a size and normal form to be received substantially wholly within either subchamber and to substantially fill the transverse section thereof when so received, said body being resiliently deformable and being capable, by virtue of such deformation, of passing through the constriction from one subchamber to the other,

means actua'ble to produce a fluid pressure differential between the respective ends of the chamber selectively in either direction to shift the body to the subchamber of lower pressure,

and sensing means associated with at least one subchamber and responsive to presence of the body therein.

2. A memory unit as defined in claim 1 and in which said body comprises a fluid mass having a surface that does not wet the chamber wall and that exerts a surface tension sufficient to prevent passage of the body between subchambers in absence of said pressure differential and to maintain unitary form of the body during such passage.

3. A memory unit as defined in claim 1, and in which said sensing means comprise a sensing passage opening into said one subchamber through a passage mouth in position to be obstructed 'when said body is in said one subchamber,

means actuable to induce fluid flow through the sensing passage,

and means for producing an output signal that is selectively responsive to presence and substantial absence of such flow.

4. A memory unit for a fluid state computer comprisstructure forming an elongated chamber having a coneither subchamber and to substantially fill the trans- 5 verse section thereof when so received, said body being resiliently deformable and being capable, by virtue of such deformation, of passing through the constriction from one subchamber to the other,

means actuable to produce a fluid pressure differential between the respective ends of the chamber selectively in either direction to shift the body to the subchamber of lower pressure,

and sensing means associated with at least one subchamber and responsive to presence of the body therein,

said body consisting of a gas bubble operating in the liquid medium, the interface between the gas and liquid having a surface tension sufficient to prevent passage of the body between subchambers in absence of said pressure diiferential and to maintain unitary form of the body during such passage.

References Cited UNITED STATES PATENTS 1,881,572 10/1932 Herz 73-401 2,746,295 5/1956 Lubkin 73398 OTHER REFERENCES D. I. Truslove, Hydraulic Memory Device, IBM Technical Disclosure Bulletin, vol. 6, N0. 3, August 1963, p, 32.

Mitchell et al., Fluid Binary Memory Cell, IBM Technical Disclosure Bulletin, vol. 8, N0. 3 August 1965, p. 4219.

RICHARD B. WILKINSON, Primary Examiner.

LAWRENCE R. FRANKLIN, Assistant Examiner.

US. Cl. X.R. 137-8 1.5 

